Compositions and methods for removal of chemical residues from metal or dielectric surfaces or for chemical mechanical polishing of a copper or aluminum surface including an aqueous solution with a pH between about 3.5 and about 7 applied for a time sufficient to remove the chemical residues.
The National Technology Roadmap for the Semiconductor Industries (1994) indicates that the current computer chips with 0.35 micron feature sizes will be reduced to 0.18 micron feature size in 2001. The DRAM chip will have a memory of 1 gigabit, and typical CPU will have 13 million transistors/cm2 (currently they only contain 4 million). The number of metal layers (the xe2x80x9cwiresxe2x80x9d) will increase from the current 2-3 to 5-6 and the operating frequency, which is currently 200 MHZ, will increase to 500 MHZ. This will increase the need for a three dimensional construction on the wafer chip to reduce delays of the electrical signals. Currently there are about 840 meters of xe2x80x9cwiresxe2x80x9d/chip, but by 2001 (without any significant design changes) a typical chip would have 10,000 meters. This length of wire would severely compromise the chip""s speed performance.
Newer methods to etch, planarize and to clean the wafers after each of these critical steps must be developed. This invention deals with a new method for treating (preparing) a wafer after a wet chemistry process step (post etch residue cleaning step, PER). Specifically this invention deals with removing residual amines from amine-based wet chemical treatment. Usually the amine based chemistries are used to remove post etch residues (xe2x80x9cpolymer residuesxe2x80x9d, xe2x80x9cfencesxe2x80x9d, vails, etc.). These chemical compositions are also applicable to post-CMP cleaning and for polishing copper and aluminum wafers in CMP planarization.
At some point during the wet chemical processing (for metal etching or post etch residue removal, etc.) of a wafer in the semiconductor industry (or flat panel displays, microelectromechanical devices, etc.) the material must xe2x80x9cmove throughxe2x80x9d a rinse step, or post clean treatment step. Such rinse steps are designed to remove the chemicals applied in the previous step and stop any further chemical effects from the previous chemicals. These solutions are also designed to reduce particulates on the substrate surfaces. Rinses are generally a two part system, i.e., one bath containing a xe2x80x9cbenignxe2x80x9d organic chemical (benign solvents simply dilute the previous amine-based chemistry, and can be isopropyl alcohol (IPA) or N-methylpyrrolidone (NMP)), followed by a water rinse, and finally a drying step which would consist of vapor IPA drying. In some facilities the product goes directly from the primary chemistry into either IPA or water. In some cases the water bath is saturated with CO2 to adjust the bath""s pH to a slightly lower pH (acidic).
As an example of the results obtained with a state of the art rinsing system, FIG. 1 is a graph of results obtained with a computer simulation by Sandia Laboratories using fluid flow equations for a Quick Dump Rinser (QDR), in which a water spray is directed onto wafer surfaces that have been treated with an amine containing wet chemistry solution, with the water from the rinse accumulating in a bath containing the wafers. The bottom of the bath is then opened to dump the accumulated water rapidly. As shown, instead of the theoretical low amine levels remaining on the wafers as indicated by curve 4, higher amine levels remain, as indicated by typical curve 6 or worst case curve 8.
Several of the current rinse solvents have low flash (IPA flash point is 22xc2x0 C., closed cup, NMP is 86xc2x0 C., closed cup) and/or SARA Title III listings. A SARA Title III listing means that the chemical must be monitored and the quantities reported to the Federal government on a yearly basis. Isopropyl alcohol and NMP are among the list of several hundred compounds.
xe2x80x9cMetal Corrosion in Wet Resist-Stripping Processxe2x80x9d, Pai, P.; Ting, C.; Lee, W.; Kuroda, R.
SEMI CMP User and Suppler Workshop; October 18-19, Austin, Tex.
Jairath, R. et al.; Proc. of Mat. Research Soc., Spring Meeting, Vol. 337, p. 121.
Fruitman, C. et al.; VMIC 1995, Santa Clara, Calif.
Scherber, D.; Planarization Technology, CMP; July 19, San Francisco, Calif.
Semiconductor Pure Water and Chemicals Seminar, Mar. 4, 1996; Santa Clara, Calif.
Kaufman, F.; J. Electrochem. Soc., 138(11), p. 3460, 1991.
Allied Signal, xe2x80x9cHydroxylamine, Redox Propertiesxe2x80x9d.
The invention solves one or more, preferably all, of the following problems common with prior art compositions and methods:
It reduces or eliminates corrosion problems
It eliminates use of flammable solvents
It eliminates SARA Title III Chemistries
It lowers mobile and transition metal ions
The post clean treatment solution of this invention has at least one of, and preferably all of, the following features:
Aqueous based
Preferably has pH between 4.2-4.4
High neutralization capacity
Designed to control mobile and transition metal xe2x80x9ctrashxe2x80x9d ions
Possible repair of metal oxide damage.
In accordance with the invention, a composition for removal of chemical residues from metal or dielectric surfaces or for chemical mechanical polishing of a copper or aluminum surface is an aqueous solution with a pH between about 3.5 and about 7. The composition contains a monofunctional, difunctional or trifunctional organic acid and a buffering amount of a quaternary amine, ammonium hydroxide, hydroxylamine, hydroxylamine salt, hydrazine or hydrazine salt base. A method in accordance with the invention for removal of chemical residues from a metal or dielectric surface comprises contacting the metal or dielectric surface with the above composition for a time sufficient to remove the chemical residues. A method in accordance with the invention for chemical mechanical polishing of a copper or aluminum surface comprises applying the above composition to the copper or aluminum surface, and polishing the surface in the presence of the composition.
In another aspect of the invention, chemical residues are removed from a metal or dielectric surface by contacting the metal or dielectric surface with an aqueous composition having a pH between about 3.5 and about 7 for a time sufficient to remove the chemical residues. In still another aspect of the invention, a copper or aluminum surface is chemical mechanical polished by applying an aqueous composition having a pH between about 3.5 and about 7 to the copper or aluminum surface, and polishing the surface in the presence of the composition.
The invention also relates to a method for removal of chemical residues from a metal or dielectric surface, by contacting the metal or dielectric surface with an aqueous composition having a pH between about 3.5 and about 7 for a time sufficient to remove the chemical residues. In one embodiment, the invention relates to a method for chemical mechanical polishing of a copper surface by applying an aqueous composition having a pH between about 3.7 and about 7 to the copper surface, and polishing the surface in the presence of the composition. In another embodiment, the invention relates to method for chemical mechanical polishing of an aluminum surface by applying an aqueous composition having a pH between about 3.7 and about 7 to the aluminum surface, and polishing the surface in the presence of the composition. The following discussion applies to each of these embodiments.
In each of the embodiments, the aqueous composition can include: a) a monofunctional, difunctional or trifunctional organic acid; and b) a buffering amount of a quaternary amine, ammonium hydroxide, hydroxylamine, hydroxylamine salt, hydrazine or hydrazine salt base.
In another alternative or additional embodiment, the aqueous composition can include a chelation agent that will complex with transition metal ions and mobile ions. In a preferred embodiment, the chelation agent includes ethylene diamine tetraacetic acid, an oxime, 8-hydroxy quinoline, a polyalkylenepolyamine or a crown ether.
In another alternative or additional embodiment, the aqueous composition can include an oxidizing agent that will maintain metal film oxide layers. In a preferred embodiment, the oxidizing agent includes ammonium peroxydisulfate, peracetic acid, urea hydroperoxide, sodium percarbonate or sodium perborate.
In one embodiment, the aqueous composition has a pH between about 4 and about 6. In another embodiment, the monofunctional, difunctional or trifunctional organic acid has the general formula: 
wherein X is xe2x80x94OH, xe2x80x94NHR, xe2x80x94H, -halogen, xe2x80x94CO2H, xe2x80x94CH2xe2x80x94CO2H, or xe2x80x94CHOHxe2x80x94CO2H and R is hydrogen or an alkyl, aryl, alkaryl or aralkyl group having from 1 to about 20 carbon atoms. In a preferred embodiment, the monofunctional, difunctional or trifunctional organic acid is selected from the group consisting of formic, acetic, propionic, n-butyric, benzoic, ascorbic, gluconic, malic, malonic, oxalic, succinic, tartaric, citric and gallic acids. In yet another preferred embodiment, the aqueous composition includes: a) a monofunctional, difunctional or trifunctional organic acid; and b) choline hydroxide.